Buglyst Blog
Learn to debug under pressure.
Playbooks for fast pattern recognition, guides for the full investigation, and articles for the engineering judgment around the edges.
17 playbooks · 509 guides · 95 articles · 12 linked practice labs ·skip to practice
Fast pattern recognition for the production failures engineers see most often.
17 playbooks
Debugging Env Var Issues
A concise checklist for incidents where local works but CI, staging, or production changes behavior.
Debugging Cache Stampedes
How to recognize and contain request spikes when cached data expires.
Debugging CORS Origin Bugs
A practical way to inspect origin parsing, credentials, and header behavior.
Debugging Retry Bugs
Retry issues often hide the first failure and create duplicate work.
Debugging Timezone Bugs
Time bugs usually live at day boundaries, DST changes, and unit conversions.
Debugging Pagination Bugs
Pagination bugs hide in boundary math, cursor reuse, and new records arriving between pages.
Structured investigations for the failure modes engineers meet in real systems.
Deployment config mismatch: how to debug environment-specific config bugs
Your staging environment works. Production does not. The code is the same but the config is different — a missing setting, a wrong endpoint, or a different feature flag value.
Feature flag bug: how to debug unexpected feature flag behaviour
A feature flag is supposed to be off for some users but is on for everyone, or vice versa. The flag value, targeting rules, or flag evaluation is wrong.
Session cookie not working after deployment: how to debug it
Users were logged in. You deploy. Everyone is logged out. The session cookie is not being sent, not being recognised, or being set with wrong attributes after the new deployment.
Redirect URL wrong in production: how to debug redirect bugs
Your app redirects users to `http://localhost:3000/dashboard` in production. The redirect URL is hardcoded, or the origin detection is picking up the wrong value.
OAuth callback URL mismatch: how to debug OAuth redirect errors
OAuth login fails with 'redirect_uri_mismatch' after deployment. The callback URL in the request does not exactly match what is registered with the OAuth provider.
Database migration works locally but fails in production: how to debug it
Your migration runs perfectly on your local database but errors out in production. Different database version, different data, or different permissions.
Long-form thinking on debugging habits, observability, and the systems around the bug.
How to Reproduce a Flaky Test: From CI Logs to Reliable Failure
A practical guide to turning intermittent test failures into reliably reproducible bugs, with techniques ranging from loop testing to thread sanitizers.
Property-Based Testing: Finding the Off-by-One That Lived in Production for 18 Months
A concrete story of how switching from example-based tests to property-based tests caught a timing bug that had survived code review, QA, and 18 months of production traffic.
How We Reduced End-to-End Test Flakiness by 80% with Deterministic Seeding
After months of chasing intermittent failures in our CI pipeline, we implemented a three-part strategy — deterministic seeding, isolated state per test, and a structured retry budget — that cut flaky end-to-end test failures by 80%.
Snapshot Testing: The 5 Hidden Failure Modes That Will Break Your CI
Snapshot tests seem like a safety net, but they often hide real bugs, bloat diffs, and silently break your CI. Here are the five failure modes I've seen in production and how to fix them.
Testing Async Code: Avoiding Flakiness and False Positives in JavaScript
Async testing is full of traps: unhandled rejections, race conditions, and tests that pass when they shouldn't. Here's how to write reliable async tests in JavaScript.
Testing Error Handling Code Paths: A Practical Approach
Error handling code is often the least tested and most brittle. Here's how to cover those paths with fault injection, mocks, and chaos engineering.